PRENATAL DIAGNOSIS, VOL.
10,787-794 (1990)
DUPLICATION OF THE LONG ARM OF CHROMOSOME 13 SECONDARY TO A RECOMBINATION I N A MATERNAL INTRACHROMOSOMAL INSERTION (SHIFT) M. VEKEMANS* AND N. MORICHON-DELVALLEZ~
*Centrefor Human Genetics. McGill University, Montreal, Canada; TLaboratoire de Cytogenetique Prenatale, Hopital Necker-Enfants Malades. Paris, France
SUMMARY 4 rare chromosomal aberration consisting of a chromosomal shift was found in a woman
who had prenatal diagnosis because she had previously had a malformed girl with phenotypic features compatible with the diagnosis of Patau syndrome. Chromosome analysis using G, C, and NOR banding showed a direct intrachromosomal insertion of bands 13ql2 to 13q14 onto the short arm of chromosome 13 at band 13pl3. We discuss this observation and compare it with other published reports of chromosomal shifts. KEY WORDS
Chromosome 13 Intrachromosomal insertion
CASE REPORT 4 24-year-old G,P,A, woman was referred to us for prenatal diagnosis because of the previous birth of a child with Patau syndrome. The female child was born to a 20-year-old mother and an unrelated 30-year-old father after an uneventful pregnancy and delivery. Her neonatal course was normal, though she was referred for cytogenic studies because of hypotrophic (birth weight: 2330 g; birth length: 44 cm; head1 circumference: 30 cm) and dysmorphic features. The head shape was abnormal with a median prominence extending over the forehead. The inner canithal distance was decreased, suggesting the presence of holoprosencephaly (not confirmed on ,iutopsy). She had microphthalmia and a cataract on the left eye, an anti-mongoloid 1;lant of palpebral fissures, and a large cleft lip with cleft palate. Also present were an appendage on the fifth finger on the right hand (post-axial polydactyly), a wide space between the first and second toes with low implantation of the first toe, and a deep plantar crease between the first and second toes. She presented irregular heart beats with occasional blue spells and died on the 15th day of life, presumably from her heart condition. Her chromosomes were examined in another laboratory and interpreted as 46,XX,t( I3ql3q). The mother reported three subsequent miscarriages, all by diifferent fathers, for which there is no information. CYTOGENETIC STUDIES Cytogenetic studies undertaken on a sample of amniotic fluid obtained at 16 weeks of gestation demonstrated that the fetus had an abnormal chromosome 13. Using Addressee for correspondence: Dr Michel Vekemans, Prenatal Diagnosis Program, The Montreal Children’s Hospital, 2300 Tupper, Montreal, Quebec, Canada H3H 1P3.
0 197--3851/90/ 120787-08$05.00 (B 1990 by John Wiley & Sons, Ltd.
Received 24 February 1990 Revised 20 July 1990 Accepted 3 August I990
788
M. VEKEMANS AND N. MORICHON-DELVALLEZ
Figure 1. Partial karyotype of the mother using GTG, CBG, and NOR banding showing the increased length of the short arm and the equivalent decreased length of the long arm in the abnomdl Chromosome 13 (46,XX,dir ins(13)p13q12q14). NOR banding shows that the stalks are located between the centramere and the shifted segment
synchronized cell cultures, further cytogenetic study was undertaken on a peripheral blood lymphocyte culture from the mother. GTG, CBG, and NOR banding techniques showed that the mother had the same abnormal chromosome 13 as the fetus and that all the other chromoso~neswere normal. In absolute length the abnormal chromosome was similar to its homologue but presented an increase in the length of the short arm and a corresponding decrease of the long arm (Figure 1). The deleted long arm material, 13q12-13q14, had been shifted to the short arm and inserted on 13~13.Both CBG and NOR banding techniques showed that the stalks mere interposed between the centromere and the shifted 13q segment. It was not possible, however, to determine on morphological data alone whether the insertion was direct or inverted. After an uneventful pregnancy, the mother delivered a healthy girl. Although a chromosome study of other members of the family was not possible, a chromosome analysis of the f,ather was performed and showed a normal male karyotype, 46,XY. Re-examination of the chromosomes of the first abnormal child established the existence of a recombinant chromosome 13 resulting presumably from a direct chromosomal shift in themother (Figure 2). Thus, the karyotype of the fetus and the mother was concluded to be 46,XX,dir ins(13)(p13qi2q14)mat (see Discussion).
DISCUSSION Shifts or interchromosomal insertions are among the rarest chromosomal abnormalities in the human species. They result from a three-break event where a
CHROMOSOME 13 LONG ARM DUPLICATION
789
Figure 2. Pedigree of the family. The phenotypically normal mother is a carrier of a balanced shift involving a direct insertion in chromosome 13 (46,XX,dir ins(13)(p13q12q14)).The first child was born with the phenotypic features of Patau syndrome. Amniocentesis during the second pregnancy showed an abnormal chromosome 13 identical to that of the mother’s. The pedigree includes only the two pregnancies from this union
transposition of a chromosomal segment to another position in the same chromosome is occurring. They may take place within one (paracentric) or between two chromosome arms (pericentric) and may be direct or inverted. Such chromosomal rearrangements carry a high reproductive risk (Daniel et al., 1989). During meiosis, to accomplish homologous pairing of loci, the bivalent forms one or two loops. In either case, crossing over within any one loop may lead to genetic imbalance (Figure 3). If the insertion is direct, as is suspected in this work, crossing over within the ‘insertional loop’ results in two recombinant chromosomes: one deficient for the segment distal to the shifted segment and the other having duplicai.ion of the same segment. Crossing over within the ‘non-insertional loop’ also results in two recombinant chromosomes, one with a deletion and the other with a duplication of the inserted segment. If the insertion is inverted, one CI-oss-overin the ‘insertional loop’ results in two unstable recombinant chromosomes, one acentric and the other one dicentric. Finally, an even number of cross-overs within a loop and/or a cross-over outside of the two loops would result in the norinal or inserted parental forms of the chromosome. Thus, to produce the duplication observed in the proband, the shift had to be direct and one cross-over would have to have occurred in the segment between 13q12 and 13q 14. Therefore, the chromosomal complements of the mother and the fetus must be 46,XX,dir ins( 13)(p13q12q 14) and the chromosomal
790
M. VEKEMANS A N D N. MORICHON-DELVALLEZ 1
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Figure 3. Diagram of the recombinant chromosome outcomes resulting from crossing over, at the fourstrand stage, in the non-insertional and/or the: insertional loops in a chromosome having a direct insertion and one having an inverted insertion. (*The ]proposed mechanism for the partial trisomy 13 observed in the proband is a direct insertion with crossing over in the insertional loop during meiosis)
complement of the proband was presumably 46,XX,rec( 13),dup(q 14-qter)dir ins( 13)(pl3q12q14)mat. From the literature, we retrieved 19 instances of intrachromosomal insertions (Table 1). Twelve were pericentric (Therkelson et al., 1973; Pan et al., 1977; Crarver et al., 1976, 1978; Palmer et al., 1977; Miller et al., 1979; Grass et al., 1981; Cohen et al., 1983; Pai et al., 1983; Martin el' af., 1985; Strobel et af., 1980; Forsytlie et al., 1988) and seven paracentric (Hoegerman, 1979; Wyandt et al., 1980; Allderdice et al., 1983; Roberts et al., 1986; Webb et al., 1988; Narahara et al., 1986; Kajii et al., 1987). Most (4/7) of the paracentric insertions were inverted. For the pericentric insertions, the orientation was direct in one case (Therkelson et al., 1973),inverted in three(Pa1meret al., 1977; Cohenetal., 1983; Strobel etal., 1980;Martinet al., 1985), and unknown in eight. This is because a recombinant chromosome with a deletion or a duplication of the shifted segment may arise through crossing over in the noninsertional loop when the insertion is direct or in the insertional loop when the insertion is inverted (Figure 3).
79 1
CHROMOSOME 13 LONG ARM DUPLICATION
Table 1. Reported cases with intrachromosomal shifts
Reference ('4) Pericentric shifts Therkelsen et al., 1973 Garver et al., 1976 Palmer et al., 1977 Pan et af., 1977 Garver et al., 1978 M[illeret al., 1979 Strobel et al., 1980 Grass et al., 1981 Cohen et al., 1983 Piii et al., 1983 M;artin et a[., 1985 Forsythe er al., 1988 This work
(13) Paracentric shifts Hoegerman, 1979 Wyandt et al., 1980 Allerdice et al., 1983 Roberts et al., 1986 Narahara et al., 1986 Kajii et al., 1987 Webb et al., 1988
Karyotype
Reason for ascertainment
dir
ins(2)(q34p13p24)pat ins( l)(p32q25q32) mat ins(l)(p22q41q25) pat ins(l)(p32q25a31) pat ins( l)(p32q25q3 I ) pat ins(7)(pl5~21q22)mat ins(1 l)(q14.5p14.2pll.2) mat ins(X)(p 1lq22q24) de n o w ins(16)(q13pl lp13) mat ins(2)(p13q31q33) pat ins(5)(p13q22q33) mat ins(1 l)(p14.2q23.3q24.2) pat ins(13)(p13q12q14)mat
Rec dup(2p) Rec del( 19) Rec dup( 19) Rec dup( 19) R'ecdup( 19) R'ecdel(7p) R'ecdup( 1 1p) In fertility RK dup( 16p) R I ~dup(2q) C R I ~dup( C 5q) R I Xdup( 1 14) RIXdup( 1 3 4
inv inv inv inv dir dir dir
ins(13)(q22q14q12)mat ins(3)(p25.5p2 1.1p 13.5) pat ins(g)(q22.1q34.3q34.1)mat/pat ins(13)(q21.3q32q31)mat ins(9)(q22.lq31.3q34.3) mat ins(9)(q22.lq31.3q34.3) mat ins(5)(p15.2p14.2p14.1)mat
R I : ~del 13q RI:C dup 3p RIXdup 9q Mental retardation Rec dup 9q Rec dup 9q Rec dup 5p
dir inv
inv
inv
In all the 19 reported cases, the cytogenetic abnormality was ascertained through a phenotypically abnormal proband. For two cases, one de n o w (Grass et af., 1981) and the other inherited (Roberts et af., 1986), the cytogenetic diagnosis was made on the carrier of a balanced intrachromosomal insertion. One involved a pericentric (Grass et af.,1981) and the other a paracentric (Roberts et af., 1986) shift. Both carriers expressed subtle phenotypical changes, gonadal dysgenesis in one case (Grass et al., 1981) and psychiatric disorders in the other (Roberts et af., 1986). In the first case (Grass et af., 198l), the cytogenetic change occurred de n o w and involved the insertion of a segment between q22 and q24 on the long arm of the X chromosome into the short arm of the same chromosome (band p l 1). To our knowled!ge, no other case of a shift involving chromosome X has been described, and whether the gonadal dysgenesis results from a submicroscopic deletion or a position efllect related to an insertion in the short arm or in the 'critical region' of the long arm of the X chromosome remains unclear. In the second case, however (Roberts et af., 1986), the authors were able to show that the mental disorder and the insertion were not associated. In 17 cases, the phenotypically abnormal proband was a carrier of an unbalanced chrosomomal complement resulting from a recombination at meiosis. The likelihood of an abnormal offspring resulting from a recomlbinant chromosome in a carrier of a shift remains difficult to evaluate. The individual chromosome,
792
M. VEKEMANS AND N. MORICHON-DELVALLEZ
its number of arms, the chromosomal site and the orientation of the shift, and other factors such as the length and the nalture of the chromosomal segment involved must be taken into account. Appropriate information to estimate the proportion of affected to unaffected siblings was available in nine sibshilps where a pericentric shift was segregating (four paternal and five maternal) and in ten sibships where a paracentric shift was segregating (three paternal and seven maternal). In the absence of information about the orientation of the shifts the data were combined. After combining cases inherited from the mother and those inherited from the father, estimated figures of 14 per cent (95 per cent confidence limits: 12-38 per cent) and 9.6 per cent (95 per cent confidence limits; &17 per cent) were obtained for the proportion of affected to normal siblings at birth for pericentric anld paracentric shifts, respectively. Owing to the small number of cases, no significant difference in the proportion of affected to normal siblings was found whether the pericentric (17 vs. 23 per cent) or the paracentric (10 vs. 6 per cent) shift was inherited maternally or paternally. Where a deficiency or a duplication for the shifted segment is observed, it results presumably from an uneven number of cross-overs in the non-insertional loop when the insertion of the shift is direct or inverted. This is expected, as in these cases a small insertional loop (< 0.8 per cent of the total haploid genome) and a large noninsertional loop (> 3 per cent of the total haploid genome) were observed. In only one instance (this work) was a duplication for the segment distal to the shifted segment observed. It therefore results from an uneven number of cross-over events in the insertional loop and confirms the presence of the direct orientation of the shift. Whether this phenomenon is related to the fact that both the insertional and the non-insertional loops were more of the same size (0.4 and 1 per cent of the total haploid genome, respectively) remains to be examined further. We also investigated whether a relationship existed between the distribution of the various breakpoints involved in the shifts described in the literature and the distribution of the fragile sites and/or the position of chiasmata, and this relationship was not observed. In addititon, we examined whether the distribution of breaks observed in the 19 reported cases were random throughout the chromosomal complement. The distribution of breakpoints was examined by making use of computer simulations according to the Monte Carlo method. Using this methodology, we found that 12 chromosomal bands were preferentially broken during the shift formation: lp32, lq25, lq31, lq32, 2p13, 5 ~ 1 45q22, , 9q34, 1 3 ~ 1 3 13q32, , 16q13, and Xq24. Interestingly enough, one of these bands was involved in the shift described in the present report. The nature of this association remains obscure, but it is known that nucleolar organizing regions are frequently involved in recombinogenic events (Erickson and Schmickel, 1985; Wilson et al., 1987). The use of conspicuous phenotypic differences has been helpful in the clinical delineation of either proximal or distal trisomy 13. The findings of persistent fetal haemoglobin and an increased number of nuclear projections on neutrophils are consistent findings associated with duplication of a proximal segment of chromosome 13. The physical features of polydactyly and haemangioma provide differential diagnosis for a distal duplicated segment of chromosome 13. As the proband has a 46,XX,dir ins( 13)(p13q12q14) karyotype, she was therefore aneuploid for the segment distal to the shift, i.e., the segment 13q14-13qter. Among
CHROMOSOME I 3 LONG ARM DUPLICATION
793
the other dysmorphic features observed, the patient presented with cleft lip and palate, microphthalmia, polydactyly, and haemangioma, suggesting again the diagnosis of duplication for the distal segment of chromosome 13, in good correlation with the cytogenetic interpretation. ACKNOWLEDGEMENTS
Pie would like to thank Dr Marc De Braekeleer for the computer simulations using the Monte Carlo method and Helene Scarpelli for her technical assistance.
REFERENCES Allderdice, P.W., Eales, B., Onyett, H., Sprague, W., Henderson, K., Lefeuvre, P.A., Pal, G. (1983). Duplication 9q34 syndrome, Am. J . Hum. Genet., 35, 1005-1019. Cohen, M.M., Lerner, C., Balkin, N.E. (1983). Duplication of 16p from insertion of 16p into 16q with subsequent duplication due to crossing over within the inserted segment, Am. J. Med. Genet., 14,89-96. Daniel, A,, Hook, E., Wulf, G. (1989). Risks of unbalanced progeny at amniocentesis to carriers of chromosome rearrangements: data from United States and Canadian laboratories, Am. J . Med. Genet., 33, 14-53, Erickson, J.M., Schmickel, R.D. (1985). A molecular basis for discrete size variation in human ribosomal DNA, Am. J. Hum. Genet., 37,3 11-325. Forsythe, G.M., Walker, H., Weiss, L., Roberson, J.R., Worsham, M.J., Babu, V.R., Van Dyke, D.L. ( 1 988). Duplication and deletion 1 lq23324 recombinants in two offspring of an intrachromosomal insertion (‘Shift’) carrier, Henry Ford Hosp. Med. J., 36,183-186. Garver, K.L., Ciocco, A.M., Turack, N.A. (1976). Partial monosomy or trisomy resulting from crossing over within a rearranged chromosome I , Clin.Genet., 10,3 19-324. Garver, K.L., Marchese, A.G., Fatora, S.R., Pan, S.F. (1978). Reproductive outcome in a family with an inherited deletion-insertion of chromosome 1, Am. J . Obstet. Gynecol., 131,345-346. Grass, F.S., Schmartz, R.P., Deal, J.O., Parke, J.C., Jr. (1981). Gonadal dysgenesis, intra-X chromosome insertion, and possible position effect in an otherwise normal female, Clin. Genet., 20,28--35. Hoegerman, S.F. (1979). Chromosome 13 long arm interstitial deletion may result from maternal inverted insertion, Science, 205, 1035-1036. Kajii, T., Matsuura, S., Murano, I., Kuwano, A. (1987). Inverted insertion (Y)(q34.3q22.3q21.2) and its recombination product: duplication 9q21 .q22.3, Jpn. J. Hum. Genet., 32,4548. Martin, N.J., Cartwright, D.W., Harvey, P.J. (1985). Duplication 5q(5q22-5q33): from an intrachromosomal insertion. Am. J. Med. Genet., 2 0 , 5 7 4 2 . Miller, M., Kaufman, G., Reed, G., Bilenker, R., Schinzel, A. (1979). Familial, balanced insertional translocation of chromosome 7 leading to offspring with deletion and duplication ofthe inserted segment, 7 ~ 1 5 - 7 ~ 2 1A,m . J. Med. Genet., 4,3123-332. Narahara, K., Takahashi, Y., Kikkawa, K., Wakita, Y., Kimura, S., Kiimoto, H. (1986). 4ssignment of ABO locus to 9q31.3-qter by study of a family in which an intrachromosomal shift involving chromosome 9 is segregating, Jpn. J . Hum. Genet., 31, 189-296. Pai, G.S., Rogers. J.F., Sommer, A. (1983). Identical multiple congenital anomalies/mental retardation (MCA/MR) syndrome due to de1(2)(q32)in two sisters with intrachromosomal insertional translocation in their father, Am. J . Med. Genet., 14, 189-1958. Palmer, C.G., Christian, J.C., Merritt, A.D. (1977). Partial trisomy 1 due to a ‘shift’ and probable location of the Duffy (Fy) locus, J . Hum. Genet., 29,371-377. Pan. S.F., Fatora. S.R., Sorg, R., Garver, K.L., Steele, M.W. (1977). Meiotic consequences of an intrachromosomal insertion of chromosome No. 1: a family pedigree, Genetics, 12, 303-3 13.
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Roberts, S.H.,Cowie, V.A., Singh, K.R. (1986). Intrachromosomal insertion ofchromosome 13 in a family with psychosis and mental subnormality, J . Ment. Defic. Res., 30,227-232. Strobel, R.J., Riccardi, V.M., Ledbetter, D.H., Hittner, H.M. (1980). Duplication 1 Ipll.3-14.1 to meiotic crossing-over, Am. J . Med. Genet., 7, 15-20. Therkelsen, A.J., Hulten, M., Jonnasson, J., Lindsten, J., Christensen, N.C., Iversen, T. (1973). Presumptive direct insertion within chromosome 2 in man, Ann. Hum. Geiiet., 36, 367-313. Webb, G.C., Voullaire, L.E., Rogers, J.G. (1988). Duplication of a small segment of 5pdue to maternal recombination within a paracentric shift, Am. J . Med. Genet., 30,875-881, Wilson, G.N., Mian, A., de Chadarevian, J.P.,Vekemans, M. (1987). Effect of aneuploidy and neoplasia on human ribosomal DNA inheritance, Am. J. Med. Genet. Suppl., 3, 121-1 32. Wyandt, H.E., Kasprzak, R., Ennis, J., Willson, K., Koch, V., Schnatterly, P., Wilson, W.. Kelly, T.E. (1980). Interstitial 3p deletion in a child due to paternal paracentric inserted inversion, Am. J. Hum. Genet., 32,13-735.
10,787-794 (1990)
DUPLICATION OF THE LONG ARM OF CHROMOSOME 13 SECONDARY TO A RECOMBINATION I N A MATERNAL INTRACHROMOSOMAL INSERTION (SHIFT) M. VEKEMANS* AND N. MORICHON-DELVALLEZ~
*Centrefor Human Genetics. McGill University, Montreal, Canada; TLaboratoire de Cytogenetique Prenatale, Hopital Necker-Enfants Malades. Paris, France
SUMMARY 4 rare chromosomal aberration consisting of a chromosomal shift was found in a woman
who had prenatal diagnosis because she had previously had a malformed girl with phenotypic features compatible with the diagnosis of Patau syndrome. Chromosome analysis using G, C, and NOR banding showed a direct intrachromosomal insertion of bands 13ql2 to 13q14 onto the short arm of chromosome 13 at band 13pl3. We discuss this observation and compare it with other published reports of chromosomal shifts. KEY WORDS
Chromosome 13 Intrachromosomal insertion
CASE REPORT 4 24-year-old G,P,A, woman was referred to us for prenatal diagnosis because of the previous birth of a child with Patau syndrome. The female child was born to a 20-year-old mother and an unrelated 30-year-old father after an uneventful pregnancy and delivery. Her neonatal course was normal, though she was referred for cytogenic studies because of hypotrophic (birth weight: 2330 g; birth length: 44 cm; head1 circumference: 30 cm) and dysmorphic features. The head shape was abnormal with a median prominence extending over the forehead. The inner canithal distance was decreased, suggesting the presence of holoprosencephaly (not confirmed on ,iutopsy). She had microphthalmia and a cataract on the left eye, an anti-mongoloid 1;lant of palpebral fissures, and a large cleft lip with cleft palate. Also present were an appendage on the fifth finger on the right hand (post-axial polydactyly), a wide space between the first and second toes with low implantation of the first toe, and a deep plantar crease between the first and second toes. She presented irregular heart beats with occasional blue spells and died on the 15th day of life, presumably from her heart condition. Her chromosomes were examined in another laboratory and interpreted as 46,XX,t( I3ql3q). The mother reported three subsequent miscarriages, all by diifferent fathers, for which there is no information. CYTOGENETIC STUDIES Cytogenetic studies undertaken on a sample of amniotic fluid obtained at 16 weeks of gestation demonstrated that the fetus had an abnormal chromosome 13. Using Addressee for correspondence: Dr Michel Vekemans, Prenatal Diagnosis Program, The Montreal Children’s Hospital, 2300 Tupper, Montreal, Quebec, Canada H3H 1P3.
0 197--3851/90/ 120787-08$05.00 (B 1990 by John Wiley & Sons, Ltd.
Received 24 February 1990 Revised 20 July 1990 Accepted 3 August I990
788
M. VEKEMANS AND N. MORICHON-DELVALLEZ
Figure 1. Partial karyotype of the mother using GTG, CBG, and NOR banding showing the increased length of the short arm and the equivalent decreased length of the long arm in the abnomdl Chromosome 13 (46,XX,dir ins(13)p13q12q14). NOR banding shows that the stalks are located between the centramere and the shifted segment
synchronized cell cultures, further cytogenetic study was undertaken on a peripheral blood lymphocyte culture from the mother. GTG, CBG, and NOR banding techniques showed that the mother had the same abnormal chromosome 13 as the fetus and that all the other chromoso~neswere normal. In absolute length the abnormal chromosome was similar to its homologue but presented an increase in the length of the short arm and a corresponding decrease of the long arm (Figure 1). The deleted long arm material, 13q12-13q14, had been shifted to the short arm and inserted on 13~13.Both CBG and NOR banding techniques showed that the stalks mere interposed between the centromere and the shifted 13q segment. It was not possible, however, to determine on morphological data alone whether the insertion was direct or inverted. After an uneventful pregnancy, the mother delivered a healthy girl. Although a chromosome study of other members of the family was not possible, a chromosome analysis of the f,ather was performed and showed a normal male karyotype, 46,XY. Re-examination of the chromosomes of the first abnormal child established the existence of a recombinant chromosome 13 resulting presumably from a direct chromosomal shift in themother (Figure 2). Thus, the karyotype of the fetus and the mother was concluded to be 46,XX,dir ins(13)(p13qi2q14)mat (see Discussion).
DISCUSSION Shifts or interchromosomal insertions are among the rarest chromosomal abnormalities in the human species. They result from a three-break event where a
CHROMOSOME 13 LONG ARM DUPLICATION
789
Figure 2. Pedigree of the family. The phenotypically normal mother is a carrier of a balanced shift involving a direct insertion in chromosome 13 (46,XX,dir ins(13)(p13q12q14)).The first child was born with the phenotypic features of Patau syndrome. Amniocentesis during the second pregnancy showed an abnormal chromosome 13 identical to that of the mother’s. The pedigree includes only the two pregnancies from this union
transposition of a chromosomal segment to another position in the same chromosome is occurring. They may take place within one (paracentric) or between two chromosome arms (pericentric) and may be direct or inverted. Such chromosomal rearrangements carry a high reproductive risk (Daniel et al., 1989). During meiosis, to accomplish homologous pairing of loci, the bivalent forms one or two loops. In either case, crossing over within any one loop may lead to genetic imbalance (Figure 3). If the insertion is direct, as is suspected in this work, crossing over within the ‘insertional loop’ results in two recombinant chromosomes: one deficient for the segment distal to the shifted segment and the other having duplicai.ion of the same segment. Crossing over within the ‘non-insertional loop’ also results in two recombinant chromosomes, one with a deletion and the other with a duplication of the inserted segment. If the insertion is inverted, one CI-oss-overin the ‘insertional loop’ results in two unstable recombinant chromosomes, one acentric and the other one dicentric. Finally, an even number of cross-overs within a loop and/or a cross-over outside of the two loops would result in the norinal or inserted parental forms of the chromosome. Thus, to produce the duplication observed in the proband, the shift had to be direct and one cross-over would have to have occurred in the segment between 13q12 and 13q 14. Therefore, the chromosomal complements of the mother and the fetus must be 46,XX,dir ins( 13)(p13q12q 14) and the chromosomal
790
M. VEKEMANS A N D N. MORICHON-DELVALLEZ 1
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Figure 3. Diagram of the recombinant chromosome outcomes resulting from crossing over, at the fourstrand stage, in the non-insertional and/or the: insertional loops in a chromosome having a direct insertion and one having an inverted insertion. (*The ]proposed mechanism for the partial trisomy 13 observed in the proband is a direct insertion with crossing over in the insertional loop during meiosis)
complement of the proband was presumably 46,XX,rec( 13),dup(q 14-qter)dir ins( 13)(pl3q12q14)mat. From the literature, we retrieved 19 instances of intrachromosomal insertions (Table 1). Twelve were pericentric (Therkelson et al., 1973; Pan et al., 1977; Crarver et al., 1976, 1978; Palmer et al., 1977; Miller et al., 1979; Grass et al., 1981; Cohen et al., 1983; Pai et al., 1983; Martin el' af., 1985; Strobel et af., 1980; Forsytlie et al., 1988) and seven paracentric (Hoegerman, 1979; Wyandt et al., 1980; Allderdice et al., 1983; Roberts et al., 1986; Webb et al., 1988; Narahara et al., 1986; Kajii et al., 1987). Most (4/7) of the paracentric insertions were inverted. For the pericentric insertions, the orientation was direct in one case (Therkelson et al., 1973),inverted in three(Pa1meret al., 1977; Cohenetal., 1983; Strobel etal., 1980;Martinet al., 1985), and unknown in eight. This is because a recombinant chromosome with a deletion or a duplication of the shifted segment may arise through crossing over in the noninsertional loop when the insertion is direct or in the insertional loop when the insertion is inverted (Figure 3).
79 1
CHROMOSOME 13 LONG ARM DUPLICATION
Table 1. Reported cases with intrachromosomal shifts
Reference ('4) Pericentric shifts Therkelsen et al., 1973 Garver et al., 1976 Palmer et al., 1977 Pan et af., 1977 Garver et al., 1978 M[illeret al., 1979 Strobel et al., 1980 Grass et al., 1981 Cohen et al., 1983 Piii et al., 1983 M;artin et a[., 1985 Forsythe er al., 1988 This work
(13) Paracentric shifts Hoegerman, 1979 Wyandt et al., 1980 Allerdice et al., 1983 Roberts et al., 1986 Narahara et al., 1986 Kajii et al., 1987 Webb et al., 1988
Karyotype
Reason for ascertainment
dir
ins(2)(q34p13p24)pat ins( l)(p32q25q32) mat ins(l)(p22q41q25) pat ins(l)(p32q25a31) pat ins( l)(p32q25q3 I ) pat ins(7)(pl5~21q22)mat ins(1 l)(q14.5p14.2pll.2) mat ins(X)(p 1lq22q24) de n o w ins(16)(q13pl lp13) mat ins(2)(p13q31q33) pat ins(5)(p13q22q33) mat ins(1 l)(p14.2q23.3q24.2) pat ins(13)(p13q12q14)mat
Rec dup(2p) Rec del( 19) Rec dup( 19) Rec dup( 19) R'ecdup( 19) R'ecdel(7p) R'ecdup( 1 1p) In fertility RK dup( 16p) R I ~dup(2q) C R I ~dup( C 5q) R I Xdup( 1 14) RIXdup( 1 3 4
inv inv inv inv dir dir dir
ins(13)(q22q14q12)mat ins(3)(p25.5p2 1.1p 13.5) pat ins(g)(q22.1q34.3q34.1)mat/pat ins(13)(q21.3q32q31)mat ins(9)(q22.lq31.3q34.3) mat ins(9)(q22.lq31.3q34.3) mat ins(5)(p15.2p14.2p14.1)mat
R I : ~del 13q RI:C dup 3p RIXdup 9q Mental retardation Rec dup 9q Rec dup 9q Rec dup 5p
dir inv
inv
inv
In all the 19 reported cases, the cytogenetic abnormality was ascertained through a phenotypically abnormal proband. For two cases, one de n o w (Grass et af., 1981) and the other inherited (Roberts et af., 1986), the cytogenetic diagnosis was made on the carrier of a balanced intrachromosomal insertion. One involved a pericentric (Grass et af.,1981) and the other a paracentric (Roberts et af., 1986) shift. Both carriers expressed subtle phenotypical changes, gonadal dysgenesis in one case (Grass et al., 1981) and psychiatric disorders in the other (Roberts et af., 1986). In the first case (Grass et af., 198l), the cytogenetic change occurred de n o w and involved the insertion of a segment between q22 and q24 on the long arm of the X chromosome into the short arm of the same chromosome (band p l 1). To our knowled!ge, no other case of a shift involving chromosome X has been described, and whether the gonadal dysgenesis results from a submicroscopic deletion or a position efllect related to an insertion in the short arm or in the 'critical region' of the long arm of the X chromosome remains unclear. In the second case, however (Roberts et af., 1986), the authors were able to show that the mental disorder and the insertion were not associated. In 17 cases, the phenotypically abnormal proband was a carrier of an unbalanced chrosomomal complement resulting from a recombination at meiosis. The likelihood of an abnormal offspring resulting from a recomlbinant chromosome in a carrier of a shift remains difficult to evaluate. The individual chromosome,
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its number of arms, the chromosomal site and the orientation of the shift, and other factors such as the length and the nalture of the chromosomal segment involved must be taken into account. Appropriate information to estimate the proportion of affected to unaffected siblings was available in nine sibshilps where a pericentric shift was segregating (four paternal and five maternal) and in ten sibships where a paracentric shift was segregating (three paternal and seven maternal). In the absence of information about the orientation of the shifts the data were combined. After combining cases inherited from the mother and those inherited from the father, estimated figures of 14 per cent (95 per cent confidence limits: 12-38 per cent) and 9.6 per cent (95 per cent confidence limits; &17 per cent) were obtained for the proportion of affected to normal siblings at birth for pericentric anld paracentric shifts, respectively. Owing to the small number of cases, no significant difference in the proportion of affected to normal siblings was found whether the pericentric (17 vs. 23 per cent) or the paracentric (10 vs. 6 per cent) shift was inherited maternally or paternally. Where a deficiency or a duplication for the shifted segment is observed, it results presumably from an uneven number of cross-overs in the non-insertional loop when the insertion of the shift is direct or inverted. This is expected, as in these cases a small insertional loop (< 0.8 per cent of the total haploid genome) and a large noninsertional loop (> 3 per cent of the total haploid genome) were observed. In only one instance (this work) was a duplication for the segment distal to the shifted segment observed. It therefore results from an uneven number of cross-over events in the insertional loop and confirms the presence of the direct orientation of the shift. Whether this phenomenon is related to the fact that both the insertional and the non-insertional loops were more of the same size (0.4 and 1 per cent of the total haploid genome, respectively) remains to be examined further. We also investigated whether a relationship existed between the distribution of the various breakpoints involved in the shifts described in the literature and the distribution of the fragile sites and/or the position of chiasmata, and this relationship was not observed. In addititon, we examined whether the distribution of breaks observed in the 19 reported cases were random throughout the chromosomal complement. The distribution of breakpoints was examined by making use of computer simulations according to the Monte Carlo method. Using this methodology, we found that 12 chromosomal bands were preferentially broken during the shift formation: lp32, lq25, lq31, lq32, 2p13, 5 ~ 1 45q22, , 9q34, 1 3 ~ 1 3 13q32, , 16q13, and Xq24. Interestingly enough, one of these bands was involved in the shift described in the present report. The nature of this association remains obscure, but it is known that nucleolar organizing regions are frequently involved in recombinogenic events (Erickson and Schmickel, 1985; Wilson et al., 1987). The use of conspicuous phenotypic differences has been helpful in the clinical delineation of either proximal or distal trisomy 13. The findings of persistent fetal haemoglobin and an increased number of nuclear projections on neutrophils are consistent findings associated with duplication of a proximal segment of chromosome 13. The physical features of polydactyly and haemangioma provide differential diagnosis for a distal duplicated segment of chromosome 13. As the proband has a 46,XX,dir ins( 13)(p13q12q14) karyotype, she was therefore aneuploid for the segment distal to the shift, i.e., the segment 13q14-13qter. Among
CHROMOSOME I 3 LONG ARM DUPLICATION
793
the other dysmorphic features observed, the patient presented with cleft lip and palate, microphthalmia, polydactyly, and haemangioma, suggesting again the diagnosis of duplication for the distal segment of chromosome 13, in good correlation with the cytogenetic interpretation. ACKNOWLEDGEMENTS
Pie would like to thank Dr Marc De Braekeleer for the computer simulations using the Monte Carlo method and Helene Scarpelli for her technical assistance.
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Roberts, S.H.,Cowie, V.A., Singh, K.R. (1986). Intrachromosomal insertion ofchromosome 13 in a family with psychosis and mental subnormality, J . Ment. Defic. Res., 30,227-232. Strobel, R.J., Riccardi, V.M., Ledbetter, D.H., Hittner, H.M. (1980). Duplication 1 Ipll.3-14.1 to meiotic crossing-over, Am. J . Med. Genet., 7, 15-20. Therkelsen, A.J., Hulten, M., Jonnasson, J., Lindsten, J., Christensen, N.C., Iversen, T. (1973). Presumptive direct insertion within chromosome 2 in man, Ann. Hum. Geiiet., 36, 367-313. Webb, G.C., Voullaire, L.E., Rogers, J.G. (1988). Duplication of a small segment of 5pdue to maternal recombination within a paracentric shift, Am. J . Med. Genet., 30,875-881, Wilson, G.N., Mian, A., de Chadarevian, J.P.,Vekemans, M. (1987). Effect of aneuploidy and neoplasia on human ribosomal DNA inheritance, Am. J. Med. Genet. Suppl., 3, 121-1 32. Wyandt, H.E., Kasprzak, R., Ennis, J., Willson, K., Koch, V., Schnatterly, P., Wilson, W.. Kelly, T.E. (1980). Interstitial 3p deletion in a child due to paternal paracentric inserted inversion, Am. J. Hum. Genet., 32,13-735.
